For requirement of low power consumption and simulation of natural light reflection display, some display screens, such as bi-stable liquid crystal display screens, do not emit light and do not transmit light itself. Display screens of this kind are usually applied to electronic books for text display or electronic demoboards, and etc. Display screens of this kind cannot provide a display source by a backlight source due to its own characteristic limitation, and need an external light source which reflects natural light or lamp light to obtain a good effect of screen display. Therefore, display screens of such type can only be used in the day time or under a condition of presence of an additional illumination source, while under conditions of dark environment or without a light source, they cannot display normally.
To make the bi-stable liquid crystal display screen able to display normally under conditions of dark environment or without a light source, a front light source is usually required to be disposed at the front end of the bi-stable liquid crystal display screen. Typically, a light emitting diode (LED) light source for illumination is additionally provided at the periphery of the bi-stable liquid crystal display screen. In this way, illumination of the display screen can be achieved, but there is a defect of inhomogeneous illumination and a bright spot is formed at a position where the LED light source is disposed. Therefore, the conventional solution can eliminate the limitation to operation environment of the bi-stable liquid crystal display screen, while the display effect of the bi-stable liquid crystal display screen is unsatisfactory.